Polyethylene terephthalate resin compositions have excellent mechanical characteristics, heat characteristics, chemical resistance, electrical characteristics, and formability, are widely used for various applications, and are demanded in increasing quantity. Along with the expansion of the applications and demand, however, the characteristics and productivity that the polyesters need are more and more stringent in each application field.
Whenever processed into a form, a polyethylene terephthalate resin composition is melted and extruded at a temperature of 250° C. to 300° C., which is equal to or greater than the melting point of the polyester, but this temperature condition will also cause the polyester to undergo thermal decomposition and then oxidative decomposition if contaminated with oxygen. There is a problem in that this results in generating gelatinous foreign matter and causes defects on the surface of the film.
JP 2003-96280 A describes polyethylene terephthalate resin compositions in which a ratio of the amount of alkaline earth metal and alkali metal to the amount of a phosphorus compound, M/P, is within a specific range. JP 11-21337 A and JP 2014-22027 A describe polyesters and polyester films for which manganese acetate is used.
A polyethylene terephthalate resin composition described in JP '280 is regulated at a high M/P to thereby have a gelation ratio reduced when left to stand under the conditions of a 20% oxygen concentration and 300° C. for 5 hours, but a high M/P will accelerate thermal decomposition and fails to afford sufficient heat resistance to the composition. In addition, magnesium acetate is used therefore and thus the gelation ratio is no more reduced in a further long time.
JP '337 describes Examples in which manganese acetate is used, and a sufficient gelation suppression effect is not obtained because the M/P is high.
JP '027 also describes Examples in which manganese acetate is used, but a large amount of antimony is used, which poses a concern about solution haze and defects caused by antimony. In addition, the gelation ratio is not expected to be improved sufficiently.
It could therefore be helpful to provide a polyethylene terephthalate resin composition that generates less gelled matter in a melt-extruding process, causes a smaller change in color tone and a smaller amount of oligomer generation during heating, and has excellent transparency (solution haze) and film formability.